Image forming device

Abstract

To prevent the occurrence of toner fusion on a surface of a photoreceptor, while extending the life of the photoreceptor.SOLUTION: An image forming apparatus 100 has a photoreceptor 1, an electrifying device 2, a developing device 4, a transfer device 5, and a cleaning device 6. The cleaning device 6 includes a cleaning blade 61, a rotatable roller-shaped brush 62, and an application unit E5 that applies a bias to the brush 62. When a tensile strength of a single fiber of brush fibers of the brush 62 in an environment of a temperature of 23°C and a humidity of 50% is defined as A (cn / dtex), a thickness of the single fiber of the brush fibers as B (denier), a flocking density per single fiber of the brush fibers as C (kF / inch2), and a length of the brush fibers as D (mm), and an elastic deformation rate of a surface of the photoreceptor 1 as E(%) when a hardness test is carried out by using a Vickers quadrangular pyramid diamond indenter in an environment of a temperature of 23°C and a humidity of 50%, 48(%)≤E≤60(%) and 400≤{A×B2×C / D2}≤20408 are satisfied.SELECTED DRAWING: Figure 5

Description

[Technical Field]

[0001] The present invention relates to an image forming apparatus such as a copying machine, a printer, or a facsimile machine that uses an electrophotographic system. [Background technology]

[0002] In conventional electrophotographic image forming apparatuses, a toner image formed on the surface of a photoreceptor through the processes of charging, exposure, and development is transferred directly to a recording material or transferred to the recording material via an intermediate transfer member. After the toner image transfer process from the photoreceptor to the receiving recording material or intermediate transfer member, untransferred toner (transfer residual toner), toner additives, discharge products, and other residues remain on the surface of the photoreceptor. Therefore, these must be removed from the surface of the photoreceptor prior to the next image formation process. Various methods for removing transfer residual toner and other residues from the surface of the photoreceptor have been used, including methods using a fur brush, a magnetic brush, and a cleaning blade. Among these, the method of scraping the photoreceptor surface with a cleaning blade to remove the transfer residual toner from the photoreceptor surface is widely used due to its relatively simple configuration and low cost.

[0003] In recent years, with the increasing speed and image quality of image forming devices, the toner used has a lower melting point and is becoming more spherical, making it difficult to ensure cleaning performance with a cleaning blade alone. To address this issue, a cleaning auxiliary device is used to assist the cleaning blade in removing residual toner after transfer. For example, a method has been proposed in which a fur brush (brush roller) that can be biased and that contacts the surface of the photoreceptor is placed upstream of the cleaning blade in the direction of movement of the surface of the photoreceptor (Patent Document 1). This method allows the fur brush to remove at least a portion of the residual toner before it reaches the cleaning blade, thereby reducing the load on the cleaning blade and improving cleaning performance.

[0004] In recent years, thermosetting photoreceptors have been developed with a surface that is less susceptible to abrasion in order to extend the life of the photoreceptor. Accordingly, there is a trend toward extending the replacement interval for cleaning blades in line with the photoreceptor. If the surface of a photoreceptor is less susceptible to abrasion, the cleaning blade is more likely to experience damage such as chattering or flipping (turning up), or chipping or wear of the edge of the cleaning blade. Furthermore, if the surface of a photoreceptor is less susceptible to abrasion, it is more likely to experience phenomena known as "fusion" or "filming," in which toner components and external additives to the toner adhere to and accumulate (grow) on the surface of the photoreceptor (hereinafter simply referred to as "toner fusion"). Therefore, a method has been proposed for refreshing the surface of a photoreceptor by mechanically polishing it by contacting a fur brush with the photoreceptor upstream of the cleaning blade in the direction of movement of the photoreceptor surface (Patent Document 2).

[0005] Thus, in order to meet the recent demands for higher speeds and longer life spans, the role of fur brushes as auxiliary cleaning means for improving cleaning performance has become increasingly important. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Laid-Open No. 2009-300860 [Patent Document 2] Japanese Patent Application Laid-Open No. 2014-228849 Summary of the Invention [Problem to be solved by the invention]

[0007] Patent Document 1 describes cleaning performance, such as improving cleaning performance by specifying the density of the fur brush hairs or the resistance of the fur brush to increase the probability of contact between the fur brush and toner. Here, the fur brush also serves to polish the surface layer of the photoreceptor in addition to its cleaning function. However, Patent Document 1 does not describe polishing or abrasion of the surface layer of the photoreceptor. Patent Document 2 also does not describe the surface characteristics of the photoreceptor and the rigidity characteristics of the fur brush. Abrasion of the surface layer of the photoreceptor varies depending on the hardness of the surface layer of the photoreceptor and the fur brush hair and contact conditions.

[0008] As mentioned above, in recent years, there has been a trend toward making the surface layer of a photoreceptor harder. However, even if the surface layer of a photoreceptor is hard, if the amount of polishing or scraping of the surface layer of the photoreceptor is small, toner fusion occurs on the surface of the photoreceptor. On the other hand, if the amount of polishing or scraping of the surface layer of the photoreceptor is large, the life of the photoreceptor will be shortened. This is because scratches in the circumferential direction of the surface layer of the photoreceptor increase, resulting in a high surface roughness and problems such as poor cleaning.

[0009] SUMMARY OF THE INVENTION An object of the present invention is to achieve a longer life of the photoreceptor while suppressing the occurrence of toner fusion on the surface of the photoreceptor. [Means for solving the problem]

[0010] The above object is achieved by an image forming apparatus according to the present invention. In summary, the present invention provides a cleaning device for cleaning the photoreceptor, the cleaning device comprising: a rotatable photoreceptor; an image forming unit for forming a toner image on the photoreceptor; a blade for contacting the photoreceptor at a first contact portion and cleaning the photoreceptor; and a rotatable brush for contacting the photoreceptor at a second contact portion located upstream of the first contact portion in the rotation direction of the photoreceptor and collecting toner remaining on the photoreceptor. a transfer device that transfers a toner image from the photosensitive member to a transfer material at a transfer position; and a static eliminator that is disposed downstream of the transfer position and upstream of the second contact portion in the rotation direction of the photosensitive member and that eliminates static electricity from the photosensitive member;The photosensitive member includes an application unit that applies a bias to the brush, and a control unit that controls the application unit, and the control unit controls the brush to apply a bias to the brush in a direction opposite to the normal charging polarity of the toner when an image forming area on the surface of the photosensitive member passes through the second contact portion. The absolute value of the potential difference between the potential of the brush and the potential of the surface of the photosensitive member neutralized by the neutralization device is 250 V or more and less than the discharge start voltage. The application unit is controlled to apply a bias to the brush so that the tensile strength of the brush is A (cn / dtex), the thickness of the brush is B (denier), and the bristle density of the brush is C (kF / inch 2 ), the length of the brush is D (mm), and the elastic deformation rate of the surface of the photosensitive member is E (%), 48 (%) ≦ E ≦ 60 (%), and 400 ≦ {A × B 2 ×C / D 2}≦20408. [Effects of the Invention]

[0011] According to the present invention, it is possible to achieve a longer life of the photoreceptor and to suppress the occurrence of toner fusion on the surface of the photoreceptor. [Brief explanation of the drawings]

[0012] [Figure 1] FIG. 1 is a schematic cross-sectional view of an image forming apparatus. [Figure 2] FIG. 2 is a schematic cross-sectional view of an image forming unit. [Figure 3] FIG. 1 is a schematic diagram of an output chart of a Fischerscope H100V (manufactured by Fischer). [Figure 4] FIG. 1 is a diagram showing an example of an output chart of a Fischerscope H100V (manufactured by Fischer). [Figure 5] 2 is a schematic cross-sectional view of the cleaning device and its surroundings in the first embodiment. FIG. [Figure 6] 1A and 1B are schematic diagrams for explaining the process of toner fusion. [Figure 7] 10A and 10B are schematic diagrams for explaining the effect of suppressing toner fusion. [Figure 8] 1 is a table showing evaluation results for Example 1. [Figure 9]FIG. 10 is a schematic cross-sectional view of the periphery of a cleaning device in a second embodiment. [Figure 10] 10 is a table showing the evaluation results for Example 2. DETAILED DESCRIPTION OF THE INVENTION

[0013] The image forming apparatus according to the present invention will be described in more detail below with reference to the drawings.

[0014] [Example 1] 1. Overall configuration and operation of the image forming apparatus 1 is a schematic cross-sectional view of an image forming apparatus 100 of this embodiment. The image forming apparatus 100 of this embodiment is a tandem four-color full-color printer that employs an intermediate transfer system and is capable of forming full-color images using an electrophotographic process.

[0015] Image forming apparatus 100 has multiple image forming units (stations): four image forming units 10Y, 10M, 10C, and 10K that form images of yellow (Y), magenta (M), cyan (C), and black (K), respectively. These image forming units 10Y, 10M, 10C, and 10K are arranged in a row along the direction of movement of the image transfer surface of intermediate transfer belt 7, which is disposed substantially horizontally, as described below. Elements in each image forming unit 10Y, 10M, 10C, and 10K that have the same or corresponding functions or configurations may be generally described by omitting the Y, M, C, or K suffixes to reference numerals indicating the element for one of the colors. Figure 2 is a schematic cross-sectional view showing one representative image forming unit 10. In this embodiment, the image forming unit 10 is configured to include photosensitive drums 1 (1Y, 1M, 1C, 1K), charging devices 2 (2Y, 2M, 2C, 2K), exposure devices 3 (3Y, 3M, 3C, 3K), developing devices 4 (4Y, 4M, 4C, 4K), primary transfer rollers 5 (5Y, 5M, 5C, 5K), cleaning devices 6 (6Y, 6M, 6C, 6K), etc., which will be described later.

[0016] The image forming apparatus 100 has a photosensitive drum 1, which is a rotatable drum-type (cylindrical) photosensitive member (electrophotographic photosensitive member) that serves as a first image carrier for carrying a toner image. A driving force is transmitted from a drum drive motor (not shown) serving as a drive source to the photosensitive drum 1, which is driven to rotate at a predetermined peripheral speed (process speed) in the direction of arrow R1 (counterclockwise) in FIG. 1 . The surface of the rotating photosensitive drum 1 is uniformly charged to a predetermined potential of a predetermined polarity (negative in this embodiment) by a charging device 2 serving as a charging means. During charging, a predetermined charging bias (charging voltage) is applied to the charging device 2 by a charging power supply (high-voltage power supply) E1. The surface of the charged photosensitive drum 1 is scanned and exposed by an exposure device 3 serving as an exposure means in accordance with an image signal, forming an electrostatic latent image (electrostatic image) on the photosensitive drum 1. The electrostatic latent image formed on the photosensitive drum 1 is developed (visualized) by the developing device 4 as a developing means, which supplies toner as a developer, and a toner image (toner image, developer image) is formed on the photosensitive drum 1. In this embodiment, toner charged with the same polarity as the charge polarity of the photosensitive drum 1 (negative polarity in this embodiment) adheres to the exposed portion (image portion) of the photosensitive drum 1, which has been uniformly charged and then exposed to light to reduce the absolute value of the potential (reverse development method). During development, a predetermined development bias (developing voltage) is applied to the developing sleeve 41 provided in the developing device 4 by the development power supply (high-voltage power supply) E2. In this embodiment, the normal charge polarity of the toner during development, which is the normal charge polarity of the toner, is negative polarity (minus, negative).

[0017] An intermediate transfer belt 7, which is a rotatable intermediate transfer body formed of an endless belt and serves as a second image carrier that carries a toner image, is disposed facing the four photosensitive drums 1Y, 1M, 1C, and 1K. The intermediate transfer belt 7 is wound around a plurality of tension rollers (support rollers), including a drive roller 71, a tension roller 72, and a secondary transfer opposing roller 73, and is stretched with a predetermined tension. The intermediate transfer belt 7 rotates (circumferentially moves) in the direction of arrow R2 (clockwise direction) in FIG. 1 at a predetermined peripheral speed corresponding to the peripheral speed of the photosensitive drums 1 when a driving force is transmitted from a belt drive motor (not shown) serving as a drive source to rotate the drive roller 71. Primary transfer rollers 5Y, 5M, 5C, and 5K, which are roller-shaped primary transfer members (transfer devices) serving as primary transfer means, are disposed on the inner circumferential surface of the intermediate transfer belt 7, corresponding to the photosensitive drums 1Y, 1M, 1C, and 1K. The primary transfer roller 5 is pressed against the photosensitive drum 1 and contacts the photosensitive drum 1 via the intermediate transfer belt 7, forming a primary transfer nip T1, which is the contact point between the photosensitive drum 1 and the intermediate transfer belt 7. The primary transfer rollers 5, all of which are tension rollers other than the drive roller 71, are driven to rotate in accordance with the rotation of the intermediate transfer belt 7. The toner image formed on the photosensitive drum 1 is transferred (primary transfer) onto the rotating intermediate transfer belt 7 by the action of the primary transfer roller 5 at the primary transfer nip T1. During primary transfer, a predetermined primary transfer bias (primary transfer voltage), which is a DC voltage of opposite polarity (positive polarity in this embodiment) to the normal charging polarity of the toner, is applied to the primary transfer roller 5 by a primary transfer power supply (high-voltage power supply) E3. For example, when forming a full-color image, the yellow, magenta, cyan, and black toner images formed on each photosensitive drum 1 are sequentially primary transferred so as to be superimposed on the same image position (image area) on the intermediate transfer belt 7.

[0018] A secondary transfer roller 8, a roller-shaped secondary transfer member serving as a secondary transfer means, is disposed on the outer peripheral surface of the intermediate transfer belt 7, facing the secondary transfer opposing roller 73. The secondary transfer roller 8 is pressed against the secondary transfer opposing roller 73 and contacts the secondary transfer opposing roller 73 via the intermediate transfer belt 7, forming a secondary transfer nip T2, which is the contact point between the intermediate transfer belt 7 and the secondary transfer roller 8. At the secondary transfer nip T2, the toner image formed on the intermediate transfer belt 7 is transferred (secondarily transferred) onto the recording material P, which is sandwiched between the intermediate transfer belt 7 and the secondary transfer roller 8, by the action of the secondary transfer roller 8. During the secondary transfer, a predetermined secondary transfer bias (secondary transfer voltage), which is a DC voltage of the opposite polarity (positive polarity in this embodiment) to the normal charging polarity of the toner, is applied to the secondary transfer roller 8 by a secondary transfer power supply (high-voltage power supply) E4. The secondary transfer opposing roller 73 is electrically grounded (connected to ground). A roller corresponding to the secondary transfer opposing roller 73 in this embodiment may be used as a secondary transfer member, and a secondary transfer voltage of the same polarity as the normal charging polarity of the toner may be applied to it. In this case, a roller corresponding to the secondary transfer roller 8 in this embodiment may be used as an opposing electrode and electrically grounded. Recording material (transfer material, recording medium, sheet) P, such as paper or a plastic sheet, is stored in a recording material cassette 11, which serves as a recording material storage unit. The recording material P stored in the recording material cassette 11 is separated and fed one by one by a feed roller 12, which serves as a feeding means. The recording material P is conveyed to a registration roller pair 14, which also serves as a conveying means, by a conveying roller pair 13, which serves as a conveying means. The recording material P is then conveyed to the secondary transfer unit T2 by the registration roller pair 14 in synchronization with the toner image on the intermediate transfer belt 7.

[0019] The recording material P onto which the toner image has been transferred is transported to a fixing device 9 serving as a fixing means. The fixing device 9 heats and pressurizes the recording material P carrying the unfixed toner image by sandwiching it between a pair of fixing rotors and transporting it, thereby fixing (melting and adhering) the toner image to the surface of the recording material P. The recording material P onto which the toner image has been fixed is discharged (output) by a pair of discharge rollers 15 serving as a discharging means or the like onto a discharge tray (not shown) or the like provided outside the main body (outside the machine) of the image forming apparatus 100.

[0020] Meanwhile, deposits such as toner remaining on the photosensitive drum 1 after the primary transfer (primary transfer residual toner) are removed from the photosensitive drum 1 by a cleaning device 6 serving as cleaning means and collected. Also, deposits such as toner remaining on the intermediate transfer belt 7 after the secondary transfer (secondary transfer residual toner) are removed from the intermediate transfer belt 7 and collected by a belt cleaning device 74 serving as intermediate transfer body cleaning means.

[0021] The position on the photosensitive drum 1 relative to the rotation direction of the photosensitive drum 1 where charging is performed by the charging device 2 is the charging position Pa. The position on the photosensitive drum 1 relative to the rotation direction of the photosensitive drum 1 where light is irradiated by the exposure device 3 is the exposure position Pb. The position on the photosensitive drum 1 relative to the rotation direction of the photosensitive drum 1 where toner is supplied by the developing device 4 (the portion facing the developing sleeve 41) is the development position Pc. The position on the photosensitive drum 1 relative to the rotation direction of the photosensitive drum 1 where primary transfer of the toner image to the intermediate transfer belt 7 is performed (corresponding to the above-mentioned primary transfer position T1, which is the contact portion with the intermediate transfer belt 7) is the primary transfer position Pd. The position on the photosensitive drum 1 relative to the rotation direction of the photosensitive drum 1 where transfer residual toner is removed by a fur brush 62 of the cleaning device 6, which will be described later (the contact portion with the fur brush 62) is the brush cleaning position Pe. Furthermore, the position on the photosensitive drum 1 (contact point with the cleaning blade 61) where the transfer residual toner is removed by a cleaning blade 61 (described later) of the cleaning device 6 in relation to the rotation direction of the photosensitive drum 1 is the blade cleaning position Pf. With respect to the rotation direction of the photosensitive drum 1, the charging position Pa, the exposure position Pb, the development position Pc, the primary transfer position Pd, the brush cleaning position Pe, and the blade cleaning position Pf are located in this order from upstream to downstream as viewed from the charging position Pa.

[0022] The image forming apparatus 100 has a CPU 201 as a control unit (control section) that controls the image forming apparatus 100. The CPU 201 is connected to a RAM 202, which serves as a storage unit used as a working memory, and a ROM 203, which serves as a storage unit that stores programs executed by the CPU 201 and various data. The CPU 201 is also connected to a video controller 204 that processes image formation information input to the image forming apparatus 100. The video controller 204, which processes image information, processes image formation information input from an external device (not shown), such as a personal computer (PC) or an image reader, connected to the image forming apparatus 100. The CPU 201 controls each section of the image forming apparatus 100 to form an image based on the image information processed and generated by the video controller 204. That is, the image forming apparatus 100 forms a toner image corresponding to the image information input to the CPU 201 on a recording material P and outputs (prints out) it.

[0023] 2.Detailed configuration of each part Next, we will explain in more detail the configuration of each part of the image forming apparatus 100. The cleaning device 6 will be explained in detail later.

[0024] <Charging device> In this embodiment, a corona charging device 2 is used as the charging means. The corona charging device 2 has a discharge electrode and a grid electrode. A high voltage is applied to the discharge electrode, and the surface of the photosensitive drum 1 is uniformly charged using a discharge phenomenon. In this embodiment, a charging power supply E1 applies a voltage to the discharge electrode so that a current of -1000 μA flows, and a voltage of -600 V is applied to the grid electrode. As a result, the surface of the rotating photosensitive drum 1 is uniformly charged to a charging potential of approximately -500 V. In this embodiment, the charging potential of the photosensitive drum 1 is negative, and the surface of the photosensitive drum 1 is charged to the negative polarity. The charging potential of the photosensitive drum 1 may be changed in conjunction with the value of the development bias based on the environment, the state of the image forming apparatus 100, and the like.

[0025] The charging means is not limited to a corona charging type charging device. For example, a contact-type charging roller that contacts the surface of the photosensitive drum 1 may be used as the charging means. In this case, the surface of the photosensitive drum 1 is charged by utilizing the discharge phenomenon that occurs in the small gap between the photosensitive drum 1 and the charging roller. In this case, a charging bias of predetermined conditions is applied to the core of the charging roller. This charging bias can be an oscillating voltage in which a direct current component (DC bias) and an alternating current component (AC bias) are superimposed. For example, the photosensitive drum 1 can be uniformly charged to approximately -500 V by setting the DC bias to -500 V and the AC bias to a peak-to-peak voltage value that is at least twice the discharge inception voltage when a DC voltage is applied in that environment.

[0026] <Exposure equipment> In this embodiment, a laser scanner was used as the exposure device 3. The exposure device 3 is equipped with a semiconductor laser, and performs image exposure based on image information on the photosensitive drum 1, the surface of which has been uniformly charged by the charging device 2. The exposure potential of the photosensitive drum 1 formed by irradiating it with laser light by the exposure device 3 is approximately -200V.

[0027] In this embodiment, an example will be described in which a semiconductor laser is used as the exposure means, but other means such as an LED may also be used.

[0028] Furthermore, a potential measuring means capable of measuring the surface potential of the photosensitive drum 1 after exposure may be provided, so that it is possible to check whether the charging potential and the exposure potential are actually at predetermined potentials.

[0029] <Developing device> In this embodiment, a developing device 4 employs a reversal development system using a two-component developer as a developing means. The developing device 4 includes a developer container 42 containing a two-component developer, which is a mixture of mainly non-magnetic toner particles (toner) and magnetic carrier particles (carrier). The developing device 4 also includes a developing sleeve 41 rotatably mounted at the opening of the developer container 42 as a developer carrier (developing member). In this embodiment, negatively charged toner (negative toner) was used as the toner. In this embodiment, the length of the developing sleeve 41 along its rotational axis is 325 mm. The developing sleeve 41 magnetically holds the developer in the developer container 42 by the action of a magnet (not shown) fixedly disposed inside the developing sleeve 41 and transports it to the developing section, which is the gap between the developing sleeve 41 and the photosensitive drum 1. In this embodiment, a developing bias, an oscillating voltage composed of a direct current (DC bias) and an alternating current (AC bias), is applied to the developing sleeve 41 by a development power source E2. For example, a developing bias in which a DC bias of -400 V and an AC bias with a Vpp of 1600 V are superimposed is applied. This developing bias causes toner to adhere to the electrostatic latent image, thereby carrying out the developing process. Note that the setting value of the developing bias is just an example, and can be set to a value that is appropriately adjusted depending on the charging potential and exposure potential of the photosensitive drum 1.

[0030] <Intermediate transfer belt> In this embodiment, an endless belt-like intermediate transfer belt 7 is used as the intermediate transfer body. In this embodiment, the intermediate transfer belt 7 has three layers, in this order from the back side (inner peripheral surface side) to the front side (outer peripheral surface side): a resin layer, an elastic layer, and a surface layer. Materials such as polyimide and polycarbonate are used as resin materials constituting the resin layer. The thickness of the resin layer is preferably 70 μm or more and 100 μm or less. Furthermore, materials such as urethane rubber and chloroprene rubber are used as elastic materials constituting the elastic layer. The thickness of the elastic layer is preferably 200 μm or more and 250 μm or less.

[0031] Furthermore, the material constituting the surface layer is preferably one that can reduce the adhesion of toner to the surface of the intermediate transfer belt 7 and improve secondary transfer properties. For example, the base material may be one type of resin material such as polyurethane, polyester, or epoxy resin, or two or more types of elastic materials such as elastic rubber (elastic rubber, elastomer), butyl rubber, etc. Then, one or more types of powder or particles such as fluororesin, or particles with different particle sizes, that reduce surface energy and increase lubricity, may be dispersed in the base material. The thickness of the surface layer is preferably 5 μm or more and 10 μm or less. In this embodiment, the intermediate transfer belt 7 is made by adding a conductive agent such as carbon black for adjusting electrical resistance, and has a volume resistivity of 1×10 8 Ω cm or more, 1×10 14 The material used was one with a resistivity of Ω·cm or less.

[0032] <Primary transfer roller> In this embodiment, the primary transfer means is a primary transfer roller 5, which is a roller formed by molding an elastic layer of hydrin rubber with adjusted electrical resistance around a metal shaft. The primary transfer roller 5 is positioned such that its center of rotation is offset approximately 2 mm downstream from the center of rotation of the photosensitive drum 1 in the direction of movement of the surface of the intermediate transfer belt 7, and is pressed toward the photosensitive drum 1 with a predetermined pressure. A primary transfer bias is applied to the primary transfer roller 5, transferring the toner image from the photosensitive drum 1 to the intermediate transfer belt 7. During this transfer, a small amount of carrier may be present on the photosensitive drum 1 in addition to the toner. Providing an elastic layer on the intermediate transfer belt 7 as described above reduces damage to the photosensitive drum 1 at the primary transfer portion T1, even if a hard object such as a carrier is sandwiched between the primary transfer portion T1 and the intermediate transfer belt 7.

[0033] <Toner> In this example, the toner is negatively charged by friction with the carrier. In this example, the carrier contains ferrite and has an average particle size of approximately 40 μm. The toner used in this example was a toner with an average particle size of approximately 6 μm, obtained by kneading a polyester-based resin binder with pigment and wax components, and then pulverizing and classifying the resulting mixture. In this example, multiple external components (external additives) were attached to the surface of the toner for purposes such as charge control, fluidity, and transferability improvement. In this example, in addition to silica and titanium oxide, inorganic fine particles with a primary particle average particle size of 30 nm to 300 nm, at least one of a cubic particle shape and a rectangular parallelepiped particle shape, and perovskite crystals were externally added. In this example, strontium titanate fine powder was externally added as the inorganic fine particles with perovskite crystals. The externally added component is preferably added in an amount of 0.05 parts by mass or more and 2.00 parts by mass or less per 100 parts by mass of the final toner particles before adding the externally added component to the toner particles, and in this example, 0.5 parts by mass of strontium titanate fine powder was externally added. It is more preferable that the strontium titanate used as the inorganic fine particles is a particle that has not been subjected to a sintering process.

[0034] This strontium titanate fine powder has at least one of a cubic particle shape and a rectangular parallelepiped particle shape, and when supplied to a cleaning section of the photosensitive drum 1 by a cleaning device 6 described later, it serves to polish the surface of the photosensitive drum 1. The material of the inorganic fine particles may be barium titanate fine powder, calcium titanate fine powder, or the like, in addition to strontium titanate.

[0035] The inorganic fine powder of perovskite crystal used in this embodiment has an average primary particle size of 30 nm or more and 300 nm or less, preferably 40 nm or more and 300 nm or less, and more preferably 40 nm or more and 250 nm or less. If this average particle size is less than 30 nm, the polishing effect of the particles in the cleaning portion of the photosensitive drum 1 by the cleaning device 6 may be insufficient. On the other hand, if this average particle size exceeds 300 nm, the polishing effect may be too strong, and scratches may occur on the surface of the photosensitive drum 1.

[0036] Furthermore, the inorganic fine powder of perovskite crystals does not necessarily exist as primary particles on the surface of the toner particles, but may exist as aggregates. Even in this case, good results can be obtained as long as the content of aggregates having a particle size of 600 nm or more is 1% by number or less. If the content of particles and aggregates having a particle size of 600 nm or more exceeds 1% by number, scratches may occur on the surface of the photosensitive drum 1 even if the primary particle size is less than 300 nm.

[0037] The cleaning portion of the photosensitive drum 1 by the cleaning device 6 includes a blade cleaning position Pf where the photosensitive drum 1 comes into contact with the cleaning blade 61, and a brush cleaning position Pe where the photosensitive drum 1 comes into contact with the fur brush 62.

[0038] Here, the average particle size (number average particle size) of the primary particles of the inorganic fine particles (external additive) can be determined by observing the inorganic fine particles present on the surface of toner particles using a scanning electron microscope. A Hitachi Ultra-High Resolution Field Emission Scanning Electron Microscope S-4800 (manufactured by Hitachi, Ltd.) can be used as the scanning electron microscope. Measurements can be performed after confirming the material of each particle through elemental analysis using an energy dispersive X-ray analyzer (manufactured by EDAX). For example, the number average particle size can be determined by measuring the major axis of the primary particles of 100 randomly selected inorganic fine particles in a field of view magnified up to 50,000 times. The observation magnification can be adjusted appropriately depending on the size of the inorganic fine particles.

[0039] The average particle size (weight average particle size) of the toner can be measured using a precision particle size distribution measuring device using the narrow hole electrical resistance method, "Coulter Counter Multisizer 3" (registered trademark, manufactured by Beckman Coulter, Inc.), equipped with a 100 μm aperture tube, and the accompanying dedicated software, "Beckman Coulter Multisizer 3 Version 3.51" (manufactured by Beckman Coulter, Inc.), for setting measurement conditions and analyzing measurement data, and can be calculated by analyzing the measurement data. Note that toner with an average particle size of 4 μm or more and 8 μm or less can be considered to be small particle size toner.

[0040] <Photosensitive drum> In this example, a negatively charged organic photoconductor (OPC) photosensitive drum 1 with a length of 360 mm in the direction of rotation axis and an outer diameter of 84 mm was used. In this example, the photosensitive drum 1 is configured by forming a photosensitive layer on a conductive substrate, the photoconductive layer being primarily composed of an organic photoconductor. An OPC typically comprises a conductive metal substrate, a charge generation layer made of organic materials, a charge transport layer, and a surface protection layer stacked in this order. The photosensitive drum 1 used in this example was constructed with each layer made of materials described in, for example, Japanese Patent Application Laid-Open No. 2005-43806. In this example, a photosensitive drum 1 with the outermost surface hardened using, for example, an electron beam irradiation device (EC150 / 45 / 40mA, manufactured by Iwasaki Electric Co., Ltd.) was used.

[0041] The elastic deformation rate of the surface of the photosensitive drum 1 (for example, the photosensitive drum 1 of the type cured by the electron beam) is preferably 48% or more and 65% or less. The universal hardness value (HU) of the surface of this photosensitive drum 1 is 150 N / mm 2 More than 220N / mm 2It is preferable that the elastic deformation ratio is less than the above range, or the universal hardness value (HU) is less than the above range, the surface of the photosensitive drum 1 is easily scratched, making it difficult to extend the life of the photosensitive drum 1. On the other hand, if the elastic deformation ratio is greater than the above range, or the universal hardness value (HU) is greater than the above range, the amount of scraping of the surface of the photosensitive drum 1 is too small, making it more likely that toner will melt onto the surface of the photosensitive drum 1.

[0042] In this embodiment, during image formation, the photosensitive drum 1 is rotated by a driving device (not shown) at a process speed (peripheral speed) of normally 400 mm / s.

[0043] The universal hardness (HU) and elastic deformation rate of the surface of the photosensitive drum 1 were measured (obtained through hardness testing) using a Fischerscope H100V microhardness measuring device (manufactured by Fischer) under a temperature of 23°C and humidity of 50%RH. The Fischerscope H100V is a device that continuously measures hardness by contacting an indenter with the measurement target (the peripheral surface of the photosensitive drum 1), continuously applying a load to the indenter, and directly reading the indentation depth under the load. A Vickers square pyramidal diamond indenter with a facing angle of 136° was used as the indenter. The indenter was pressed against the peripheral surface of the photosensitive drum 1, and the final load continuously applied to the indenter (final load) was 6 mN. The time (holding time) for which the final load of 6 mN was applied to the indenter was 0.1 seconds. There were 273 measurement points.

[0044] FIG. 3 shows an outline of an output chart of a Fischerscope H100V (manufactured by Fischer). FIG. 4 shows an example of an output chart of a Fischerscope H100V (manufactured by Fischer) when the photosensitive drum 1 in this embodiment is used as the measurement object. In FIGS. 3 and 4, the vertical axis represents the load F (mN) applied to the indenter, and the horizontal axis represents the indentation depth h (μm) of the indenter. FIG. 3 shows the results when the load applied to the indenter is gradually increased until it reaches a maximum (A→B), and then gradually decreased (B→C). FIG. 4 shows the results when the load applied to the indenter is gradually increased until it reaches a final load of 6 mN, and then gradually decreased.

[0045] The universal hardness value (HU) can be calculated from the indentation depth of the indenter when a final load of 6 mN is applied to the indenter using the following formula: In the formula, HU means universal hardness (HU), and F f means the ultimate load, and S f means the surface area of ​​the indenter when the final load is applied, and h f means the indentation depth of the indenter when the final load is applied. HU=F f (N) / S f (mm 2 ) =6×10 -3 / {26.43×(h f x10 -3 ) 2}

[0046] The elastic deformation rate can be calculated from the work (energy) performed by the indenter on the measurement target (the peripheral surface of the photosensitive drum 1), i.e., the change in energy due to an increase or decrease in the load of the indenter on the measurement target (the peripheral surface of the photosensitive drum 1). Specifically, the elastic deformation rate is calculated by dividing the elastic deformation work We by the total work Wt (We / Wt). The total work Wt is the area of ​​the region enclosed by ABDA in Figure 3, and the elastic deformation work We is the area of ​​the region enclosed by CBDC. These surface characteristics of the photosensitive drum 1 can be represented by the measurement results when the photosensitive drum 1 is first used (when new).

[0047] 3.Cleaning device <Overall configuration and operation of the cleaning device> Next, the cleaning device 6 in this embodiment will be described in more detail. Figure 5 is a schematic cross-sectional view of the periphery of the cleaning device 6 in this embodiment.

[0048] The cleaning device 6 has a housing 66. The cleaning device 6 also has a fur brush (conductive fur brush roller) 62, which is a rotatable, conductive roller-shaped brush. The fur brush 62 functions as a toner scraping means (cleaning member) that scrapes toner off the photosensitive drum 1, and also functions as a photosensitive member polishing means (polishing member) that polishes the surface of the photosensitive drum 1. The fur brush 62 also constitutes a cleaning auxiliary means (cleaning auxiliary member) that assists a cleaning blade 61, which will be described later, in removing toner from the surface of the photosensitive drum 1. The fur brush 62 is rotatably supported by the housing 66. The rotational axis of the fur brush 62 is approximately parallel to the rotational axis of the photosensitive drum 1. The fur brush 62 is arranged to abut against the surface of the photosensitive drum 1. In this embodiment, the fur brush 62 is arranged so that its penetration into the surface of the photosensitive drum 1 is 0.7 mm. Here, the penetration amount can be represented by a value obtained by subtracting the distance (shortest distance) between the substrate on the rotation axis of the fur brush 62 (described later) and the photosensitive drum 1 from the length of the brush fibers (described later). The fur brush 62 is rotated in the direction of arrow R3 (clockwise direction) in FIG. 5 by a driving force transmitted from a driving motor serving as a driving source while in contact with the surface of the photosensitive drum 1 at a predetermined rotation speed (the peripheral speed when the brush fibers are not deformed by an external force). In other words, the fur brush 62 is rotated so as to move in the forward direction of the photosensitive drum 1 at the contact portion with the photosensitive drum 1. Note that the fur brush 62, which is a rotating member, may receive a driving force from a dedicated driving source, or may receive a branched driving force from a driving source of another rotating member, such as the driving source of the photosensitive drum 1. In this embodiment, the fur brush 62 is rotated at a peripheral speed faster than the peripheral speed of the photosensitive drum 1 (the moving speed of the surface). In this embodiment, the fur brush 62 is rotated at a peripheral speed that is 110% of the peripheral speed of the photosensitive drum 1.

[0049] The cleaning device 6 also has a cleaning blade (elastic cleaning blade) 61, which is a plate-like (blade-like) member made of an elastic material. The cleaning blade 61 functions as a toner scraping means (cleaning member) that scrapes toner off the photosensitive drum 1, and also functions as a photosensitive-body polishing means (polishing member) that polishes the surface of the photosensitive drum 1. The cleaning blade 61 is fixed to a support member 61a made of sheet metal or the like by adhesive or the like, and this support member 61a is fixed to the housing 66, thereby being supported by the housing 66. The longitudinal direction of the cleaning blade 61 is approximately parallel to the rotational axis direction of the photosensitive drum 1. The cleaning blade 61 is positioned so as to abut against the surface of the photosensitive drum 1 at a contact portion (blade cleaning position Pf) downstream of a contact portion (brush cleaning position Pe) between the fur brush 62 and the photosensitive drum 1 in the rotation direction of the photosensitive drum 1. The cleaning blade 61 is arranged so that the edge portion of the free end portion, which is one end portion in the width direction approximately perpendicular to the longitudinal direction of the cleaning blade 61 (the edge portion on the photosensitive drum 1 side), abuts against the photosensitive drum 1 with a predetermined pressure. The cleaning blade 61 also abuts against the photosensitive drum 1 in the counter direction to the rotation direction of the photosensitive drum 1 so that the free end portion is located upstream of the fixed end portion, which is the other end portion in the width direction of the cleaning blade 61, in the rotation direction of the photosensitive drum 1.

[0050] The cleaning device 6 also has a collection roller 63, which is a rotatable, conductive roller-shaped member. The collection roller 63 functions as a collection means (collection member) that collects toner from the fur brush 62, and also functions as a voltage application means (voltage application member, conductive member) that applies a voltage to the fur brush 62. The collection roller 63 is rotatably supported by a housing 66. The rotational axis of the collection roller 63 is approximately parallel to the rotational axis of the fur brush 62. The collection roller 63 is disposed so as to contact the fur brush 62 downstream of the contact point between the fur brush 62 and the photosensitive drum 1 in the rotation direction of the fur brush 62. The contact point between the fur brush 62 and the collection roller 63 in the rotation direction of the collection roller 63 is the collection position Pg. While in contact with the fur brush 62, the collection roller 63 receives a driving force transmitted from a drive motor serving as a drive source and is rotationally driven in the direction of arrow R4 in FIG. 5 (counterclockwise direction) at a predetermined rotational speed (circumferential speed). That is, the collection roller 63 is rotationally driven so as to move in the forward direction of the fur brush 62 at the contact portion with the fur brush 62. The collection roller 63, which is a rotating member, may receive a driving force from a dedicated driving source, or may receive a branched driving force from a driving source of another rotating member, such as the driving source of the photosensitive drum 1 or the fur brush 62. In this embodiment, the collection roller 63 is rotationally driven at a circumferential speed faster than that of the fur brush 62. In this embodiment, the collection roller 63 is rotationally driven at a circumferential speed that is 105% of the circumferential speed of the fur brush 62.

[0051] Furthermore, the cleaning device 6 has a scraper member 64, which is a plate-like (blade-like) member made of an elastic material. The scraper member 64 functions as a means (removing member) for removing toner from the collection roller 63. The scraper member 64 is supported by a housing 66. Note that, like the cleaning blade 61, the scraper member 64 may be supported by the housing 66 via a support member. The longitudinal direction of the scraper member 64 is approximately parallel to the rotational axis direction of the collection roller 63. The scraper member 64 is disposed so as to abut against the surface of the collection roller 63 downstream of the contact portion (collection position Pg) between the collection roller 63 and the fur brush 62 in the rotation direction of the collection roller 63. The contact portion between the collection roller 63 and the scraper member 64 in the rotation direction of the collection roller 63 is the removal position Ph. The scraper member 64 is arranged so that an edge portion (edge ​​portion on the collection roller 63 side) of a free end portion, which is one end portion in a lateral direction approximately perpendicular to the longitudinal direction, abuts against the collection roller 63 with a predetermined pressure. The scraper member 64 also abuts against the collection roller 63 in a counter direction to the rotation direction of the collection roller 63 so that the free end portion is located upstream of the fixed end portion, which is the other end portion in the lateral direction, in the rotation direction of the collection roller 63.

[0052] The cleaning device 6 also has a conveying screw 65 as a conveying means. The conveying screw 65 is disposed below the scraper member 64 in the direction of gravity. The conveying screw 65 conveys the toner collected in the housing 66 along the rotational axis of the photosensitive drum 1, for example, from the front side to the back side of the paper in FIG. 5.

[0053] A cleaning power supply E5 is connected to the collection roller 63 as an application unit constituting a potential switching means for the fur brush 62. A cleaning bias (cleaning voltage) can be applied to the collection roller 63 by the cleaning power supply E5. The cleaning power supply E5 can also be considered a component of the cleaning device 6. The cleaning power supply E5 is connected to a CPU 201 that controls the timing and value (potential) of the bias application. In this embodiment, when cleaning the toner on the surface of the photosensitive drum 1, the cleaning power supply E5 applies a cleaning bias, which is a DC voltage of positive polarity (positive), which is opposite to the normal charging polarity of the toner, to the collection roller 63. The cleaning time is, more specifically, when the image forming area (area where a toner image can be formed) on the surface of the photosensitive drum 1 passes through a brush cleaning position Pe, which is defined for the recording material P and is related to the movement direction of the surface of the photosensitive drum 1. As will be described in detail later, a conductive material such as conductive fiber is used for the fur brush 62. The fur brush 62 comes into contact with the collection roller 63 to which a cleaning bias is applied, and thus assumes a potential whose absolute value is slightly smaller than that of the cleaning bias applied to the collection roller 63. In this way, the fur brush 62 assumes a positive potential, which is opposite to the normal charging polarity of the toner. As a result, the toner on the surface of the photosensitive drum 1 is not only mechanically captured by the fur brush 62 rubbing against the surface of the photosensitive drum 1, but also electrostatically captured. This further improves cleaning efficiency. In this way, at least a portion of the toner on the surface of the photosensitive drum 1 is collected by the fur brush 62 before it reaches the cleaning blade 61.

[0054] The toner that has moved from the surface of the photosensitive drum 1 to the fur brush 62 at the contact portion between the photosensitive drum 1 and the fur brush 62 moves to the collection roller 63 at the contact portion between the fur brush 62 and the collection roller 63 due to the potential difference between the fur brush 62 and the collection roller 63. In other words, the collection roller 63 has a potential that is slightly larger in absolute value than the fur brush 62 and that is opposite in polarity to the normal charging polarity of the toner. As a result, at least a portion of the toner collected by the fur brush 62 electrostatically moves to the collection roller 63. The toner that has moved to the collection roller 63 at the contact portion between the fur brush 62 and the collection roller 63 is scraped off the surface of the collection roller 63 by the scraper member 64 at the contact portion between the collection roller 63 and the scraper member 64. The toner scraped off the surface of the collection roller 63 by the scraper member 64 falls by gravity.

[0055] Furthermore, the toner on the surface of the photosensitive drum 1 that has not been collected by the fur brush 62 is scraped off from the surface of the photosensitive drum 1 by the cleaning blade 61 and is collected in the housing 66 .

[0056] The toner thus collected in the housing 66 is transported by the transport screw 65 disposed in the lower part (bottom) of the housing 66 and is discharged to the outside of the housing 66. Then, this toner is transported toward a collection container (not shown) provided in the main body of the image forming apparatus 100 or the like.

[0057] In this embodiment, the application of the cleaning bias to the recovery roller 63 is started in synchronization with the timing at which the charging device 2 starts driving (charging the surface of the photosensitive drum 1) after the photosensitive drum 1 starts rotating.

[0058] <Cleaning blade> The cleaning blade 61 in this embodiment is made of urethane rubber, has a length of 340 mm in the longitudinal direction, and is in contact with the photosensitive drum 1 with a predetermined contact pressure. From the viewpoint of cleaning performance, the preferred physical properties of the cleaning blade 61 are as follows: It is preferable that the hardness (IRHD) is in the range of 65° or more and 85° or less. It is also preferable that the coefficient of resilience in a 25°C environment is in the range of 15% or more and 60% or less. It is also preferable that the elongation at break in a tensile test is 300% or less. It is also preferable that the Young's modulus is 50 kg / cm. 2 More than 200kg / cm 2 It is preferable that the 100% modulus is in the range of 4.0 MPa or more and 9.0 MPa or less. It is more preferable that the hardness (IRHD) is in the range of 70° or more and 80° or less, the elongation at break in a tensile test is in the range of 250% or less, and the rebound resilience at 25°C is in the range of 15% or more and 35% or less.

[0059] The methods for measuring the above physical properties are as follows. The hardness (IRHD) of the prepared cleaning blade 61 was measured in accordance with JIS K 6253 using a Wallace hardness tester. The 100% modulus of the prepared cleaning blade 61 was measured in accordance with JIS K 6251 using a tensile tester (Unitron TS-3013) manufactured by Ueshima Seisakusho. The elongation at break in the tensile test was measured in accordance with JIS K 6251 using a tensile tester (Unitron TS-3013) manufactured by Ueshima Seisakusho. The rebound resilience of the prepared cleaning blade 61 was measured in an environment of 25°C in accordance with JIS K 6255 using a Lübke rebound resilience tester manufactured by Ueshima Seisakusho. The Young's modulus of the produced cleaning blade 61 was measured in accordance with JIS K 6251 using a tensile tester (Unitron TS-3013) manufactured by Ueshima Seisakusho.

[0060] <Fur Brush> The fur brush 62, which is a rotating member, is constructed by implanting fibers on a rotating shaft. In this embodiment, it is manufactured by wrapping a fabric material (substrate) on which fibers are implanted around a metal rotating shaft having a diameter of 12.1 mm. As an example, the fibers (brush fibers) of the fur brush 62 are made of a bundle of acrylic monofilaments having a thickness of 6 denier, with a fiber implant density of 70 kF / inch. 2 The fibers are implanted on the substrate at a density of 1 / 2000 (fiber density per single fiber). As an example, the overall outer diameter of the fur brush 62 (when the brush fibers are not deformed by external force) is 21.4 mm. The length of the brush fibers, calculated by subtracting the diameter of the core (12.1 mm) and the thickness of the substrate (0.15 mm × 2) from the outer diameter, is 4.5 mm. In this embodiment, conductive fibers are used as the brush fibers, with the electrical resistance of the fibers adjusted by dispersing a certain amount of conductive particles such as carbon as a conductive agent in the fiber matrix. From the viewpoint of cleaning performance, the preferred physical properties of the fur brush 62 are as follows: The tensile strength of a single fiber (herein simply referred to as the "tensile strength of the brush fiber") at a temperature of 23°C and a humidity of 50% is preferably in the range of 40 cn / dtex or more and 80 cn / dtex or less. If the tensile strength of the brush fibers is less than 40 cn / dtex, the fibers may collapse early, preventing the fur brush 62 from collecting toner and potentially resulting in poor cleaning. If the tensile strength of the brush fibers exceeds 80 cn / dtex, the surface of the photosensitive drum 1 may be damaged in the circumferential direction, potentially resulting in poor image quality. Furthermore, the electrical resistance of the fur brush 62 is preferably in the range of 10 Log Ω to 12 Log Ω inclusive under an environment of 23°C temperature and 50% humidity. If the electrical resistance is less than 10 Log Ω, excessive current may flow from the fur brush 62 to the photosensitive drum 1, potentially resulting in poor image quality due to drum memory (a phenomenon in which the surface potential history remains unresolved). If the electrical resistance exceeds 12 Log Ω, insufficient current may flow through the fur brush 62, potentially preventing the fur brush 62 from collecting toner.

[0061] The above physical properties were measured as follows. The tensile strength of a single fiber of the brush fiber at a temperature of 23°C and a humidity of 50% was measured in accordance with JIS L 1096:2010, Testing Methods for Woven and Knit Fabrics. The electrical resistance of the fur brush 62 was measured using a Canon-made device as follows: The fur brush 62 was brought into contact with a metal roller with a penetration depth of 1 mm, and the electric current flowing through the fur brush 62 was detected when the fur brush 62 was rotated while a voltage of 400 V was applied to the fur brush 62, thereby measuring the electrical resistance of the fur brush 62.

[0062] The conditions for the fur brush 62 that enable the occurrence of toner fusion on the surface of the photosensitive drum 1 to be suppressed while achieving a long life of the photosensitive drum 1 will be described in more detail later.

[0063] <Recovery roller> In this embodiment, the recovery roller 63 is a solid metal roller made of SUS (stainless steel) and having an outer diameter of φ13 mm.

[0064] <Scraper component> The scraper member 64 may be made of a nylon sheet material, a polyurethane rubber blade, etc. In this embodiment, substantially the same material as the cleaning blade 61 described above is used.

[0065] 4. Fur brush rigidity characteristics and photosensitive drum surface characteristics Next, we will explain the relationship between the conditions of the fur brush 62 and the surface of the photosensitive drum 1, and a configuration that can appropriately scrape the surface of the photosensitive drum 1 and suppress toner fusion while suppressing scratches on the surface of the photosensitive drum 1 to extend the life of the photosensitive drum 1.

[0066] <Occurrence and prevention of toner melting> First, the effect of suppressing toner fusion by the fur brush 62 to which a bias can be applied in this embodiment will be described. Fig. 6 is a schematic diagram for explaining the process by which toner fusion occurs. Fig. 7 is a schematic diagram for explaining the effect of suppressing toner fusion by the fur brush 62 to which a bias can be applied in this embodiment.

[0067] As shown in Figure 6, the cleaning blade 61 in contact with the photosensitive drum 1 rubs against it, causing the temperature to rise in the vicinity of the contact point between the cleaning blade 61 and the photosensitive drum 1 (also referred to as the "blade nip" here). As a result, the toner present in the vicinity of the blade nip melts and adheres to the photosensitive drum 1. Toner fusion is a phenomenon that occurs in this way.

[0068] Normally, a deposit of external additives in the toner (also called an "external additive dam layer" here) (Figure 7) forms near the blade nip, preventing the toner from entering the vicinity of the blade nip. As a result, the toner temperature rise is suppressed, and toner fusion does not occur.

[0069] However, the small particle size toner required for high image quality in recent years has high fluidity and is prone to destroying the external dam layer (Figure 6). In addition, as the process speed increases, the frictional heat generated by the cleaning blade 61 also tends to increase, making toner melting more likely to occur.

[0070] Therefore, in this embodiment, as shown in FIG. 7 , a biasable fur brush 62 is positioned upstream of the cleaning blade 61 in the direction of movement of the surface of the photosensitive drum 1, thereby collecting toner before it reaches the external dam layer. As a result, the external dam layer is stably maintained, suppressing the occurrence of toner fusion. In this embodiment, a cleaning bias of +300 V, which is opposite in polarity to the normal charging polarity of the toner, is applied to the conductive fur brush 62, thereby collecting toner using the fur brush 62. In this way, the provision of a biasable fur brush 62 can minimize the occurrence of toner fusion. However, even when a biasable fur brush 62 is provided, it is important to appropriately suppress the growth (accumulation) of toner fusion if it occurs during long-term use of a photosensitive drum 1 with a long life.

[0071] On the other hand, a conventional method has been to position a fur brush so that it abuts against the photosensitive drum upstream of the cleaning blade in the direction of movement of the photosensitive drum surface, and mechanically polish the surface of the photosensitive drum together with any adhering matter. However, if the rigidity of the fur brush is increased to improve the polishing power of the fur brush, although toner fusion is suppressed, the photosensitive drum is excessively abraded, resulting in problems such as a shortened lifespan of the photosensitive drum.

[0072] In this way, by applying a bias to increase the toner collection ability of the fur brush 62 and stably maintaining the external dam layer, it is possible to suppress the occurrence of toner fusion itself, and to make it possible to moderately polish the surface of the photosensitive drum 1 without making the rigidity of the fur brush 62 too high, thereby suppressing the growth of toner fusion while preventing the photosensitive drum 1 from shortening its lifespan.

[0073] <Relationship between fur brush conditions and the surface of the photosensitive drum> It has been found that the amount of scraping of the surface layer of the photosensitive drum 1 and whether or not toner melting occurs are affected by the conditions of the fur brush 62.

[0074] First, the abrasion of the surface of the photosensitive drum 1 and the polishing of deposits on the surface of the photosensitive drum 1 vary depending on the specifications of the fur brush 62. Therefore, fur brushes 62 with different tensile strengths, thicknesses, lengths, and planting densities of the brush fibers were created, and the relationship with the abrasion of the surface of the photosensitive drum 1 was investigated. Note that the penetration depth of the fur brush 62 into the photosensitive drum 1 was kept constant.

[0075] Here, the tensile strength of the brush fiber A [cn / dtex], the thickness of the brush fiber B [denier], and the density of the brush fiber C [kF / inch 2 ] and the brush fiber length D [mm], a brush stiffness index can be calculated as an index of the hardness of the fur brush 62 relative to the photosensitive drum 1. This brush stiffness index (unitless) is specifically expressed by the following formula (1). Brush stiffness index = A x B 2 ×C / D 2 ···(1)

[0076] The brush stiffness index in the above formula (1) is calculated by multiplying the strength of the brush fibers by the contact area. The stiffness of the brush fibers itself was checked by changing the thickness and length of the brush fibers, and it was confirmed that the stiffness increases as the brush fiber length decreases and as the brush fiber thickness increases. It can be said that the larger the brush stiffness index in the above formula (1), the harder the fur brush 62 comes into contact with the photosensitive drum 1, and the greater the rate at which the surface of the photosensitive drum 1 is scraped off. It can also be said that the larger the brush stiffness index in the above formula (1), the higher the ability to remove deposits from the surface of the photosensitive drum 1.

[0077] On the other hand, for the photosensitive drum 1 that comes into contact with the fur brush 62, photosensitive drums 1 with different surface layer hardness and elastic deformation rate E were prepared, and the abrasion of the surface layer when it comes into contact with the fur brush 62 was confirmed under multiple conditions. As a result, it was found that the elastic deformation rate has a strong correlation with surface abrasion and toner fusion.

[0078] Brush stiffness index (=A×B 2 ×C / D 2) and the elastic deformation rate (= E) of the photosensitive drum 1 can both be considered indicators of hardness. Therefore, if this ratio falls within a certain range, it is possible to keep the abrasion of the surface layer of the photosensitive drum 1 within an appropriate range when a fur brush 62 with a certain rigidity is arranged. In other words, it is possible to prevent toner melting due to insufficient abrasion of the surface layer of the photosensitive drum 1, and to prevent excessive abrasion of the surface of the photosensitive drum 1, resulting in a shortened lifespan of the photosensitive drum 1.

[0079] <Experimental Example> Brush stiffness index (=A×B 2 ×C / D 2 The following experiment was conducted by changing the surface roughness, surface abrasion, and surface roughness of the photosensitive drum 1, as well as the occurrence of image defects due to toner fusion, when 500,000 images were formed in a high-humidity, high-temperature environment (30°C / 80%). Note that the evaluation was conducted using the black image forming unit 10K.

[0080] As the wear on the surface of the photosensitive drum 1 progresses, black streaks appear on the paper on which an image was formed. If black streaks appeared on the paper among the 500,000 sheets on which images were formed, it was judged as poor (×), and if they did not appear, it was judged as good (◯). Furthermore, as toner fusion on the surface of the photosensitive drum 1 progresses, white spots (white dots) appear in the solid black image on the paper on which the image was formed. If white dots with a size (maximum diameter) of 2 mm or more appeared in the solid black image on the paper among the 500,000 sheets on which images were formed, it was judged as poor (×), and if they did not appear, it was judged as good (◯).

[0081] The results are shown in Figure 8. As an example, when the brush applied voltage is 0 V, the tensile strength A of the brush fibers of the fur brush 62 is 80 cn / dtex, the thickness B of the brush fibers is 6 denier, and the bristle density C of the brush fibers is 75 kF / inch. 2The results are described below (Experiments Nos. 1 to 5) for five different elastic deformation rates E of the photosensitive drum 1: 45%, 48%, 55%, 60%, and 62% with the brush fiber length D set to 4.5 mm. Five hundred thousand images were formed on the photosensitive drum 1 with each elastic deformation rate E, and the occurrence of abrasion of the surface of the photosensitive drum 1 and toner fusion was confirmed. As a result, when the elastic deformation rate of the photosensitive drum 1 was 45%, image defects occurred after printing approximately 480,000 sheets. This is thought to be due to the low rigidity of the photosensitive drum 1, which resulted in excessive abrasion of the surface of the photosensitive drum 1. Furthermore, when the elastic deformation rate of the photosensitive drum 1 was 48% or higher, toner fusion occurred. This is thought to be due to the high rigidity of the photosensitive drum 1, which resulted in a small amount of polishing of the surface of the photosensitive drum 1.

[0082] Next, similar experiments were conducted (Experiments Nos. 6 to 25) under the condition that the brush applied voltage was 0V, by varying the brush fiber thickness B, brush fiber density C, and brush fiber length D of the fur brush 62 to change the brush stiffness index. As a result, it was found that under the condition that the brush applied voltage was 0V, it was possible to prevent toner fusion by increasing the brush stiffness index, but scraping of the surface layer of the photosensitive drum 1 occurred early. In other words, it was not possible to set a condition that could achieve both suppression of image defects due to excessive scraping of the photosensitive drum 1 and suppression of toner fusion.

[0083] In contrast, by applying a cleaning bias (+300 V in this embodiment) to the fur brush 62 (Experiments Nos. 26 to 41), it became possible to suppress toner fusion without increasing the brush rigidity index (e.g., Experiments Nos. 27 to 29). Also, by applying a cleaning bias (+300 V in this embodiment) to the fur brush 62 (Experiments Nos. 26 to 41), it became possible to sufficiently lower the brush rigidity index, and it became possible to suppress the occurrence of image defects due to excessive scraping of the surface layer of the photosensitive drum 1. In other words, it became possible to achieve both suppression of toner fusion and a longer life of the photosensitive drum 1 (e.g., Experiments Nos. 27 to 29).

[0084] In Experiments Nos. 31 to 34, the brush fiber length D was varied in the range of 3.6 to 4.5 mm to change the brush stiffness index. In these experiments, good results were obtained when the brush fiber length D was in the range of 4.2 to 4.5 mm. In Experiments Nos. 35 to 38, the brush fiber tensile strength was set to 40 cn / dtex and the brush fiber thickness B was varied in the range of 6 to 18 denier to change the brush stiffness index. In these experiments, good results were obtained when the brush fiber thickness B was in the range of 6 to 15 denier. In Experiments Nos. 39 to 41, the brush fiber tensile strength was set to 40 cn / dtex and the brush fiber bristle density C was set to 30 to 75 kF / inch. 2 In these experiments, the brush stiffness index was changed by changing the brush fiber density C in the range of 30 to 45 kF / inch. 2 In Experiments Nos. 31 to 41, the evaluation was carried out under conditions where the photosensitive drum 1 was relatively easily scraped, with the elastic deformation rate E of the photosensitive drum 1 being 48%.

[0085] Furthermore, it has been found that if the brush rigidity index is too small, the bristles of the fur brush 62 will collapse and will not be able to properly contact the photosensitive drum 1, making it impossible for the fur brush 62 to collect the toner before it reaches the cleaning blade 61. Studies by the present inventors have shown that if the brush rigidity index is 400 or higher, such problems can be sufficiently suppressed.

[0086] From the results shown in Figure 8, the following conditional expression, 48(%)≦E≦60(%), and 400≦{A×B 2 ×C / D 2}≦20408 It can be seen that by satisfying the above condition, the following effects can be obtained: In other words, it is possible to prevent the shortening of the life of the photosensitive drum 1 due to excessive abrasion of the surface layer of the photosensitive drum 1, while also suppressing the occurrence of toner melting due to insufficient abrasion of the surface layer of the photosensitive drum 1.

[0087] In this way, when a cleaning bias is applied to the fur brush 62, the brush stiffness index (=A×B) is set to satisfy the above conditional expression. 2 ×C / D 2 ) and the elastic deformation rate (=E) of the photosensitive drum 1, it is possible to suppress the occurrence of defects such as a shortened life of the photosensitive drum 1 and toner fusion. In other words, by bringing the fur brush 62, which is of appropriate conditions in accordance with the surface hardness of the photosensitive drum 1, into contact with the photosensitive drum 1, it is possible to suppress the occurrence of image defects such as toner fusion on the surface of the photosensitive drum 1 without excessively scraping the surface of the photosensitive drum 1. In other words, according to this embodiment, the occurrence of toner fusion itself is suppressed by applying a bias to improve the toner collection ability of the fur brush 62 and stably maintaining the external dam layer, and it is possible to moderately polish the surface of the photosensitive drum 1 without making the rigidity of the fur brush 62 too high, thereby suppressing the shortened life of the photosensitive drum 1 and suppressing the growth of toner fusion.

[0088] As described above, in this embodiment, the image forming apparatus 100 has a rotatable photosensitive member 1, a charging device 2 that charges the surface of the photosensitive member 1 at a charging position Pa, a developing device 4 that supplies toner to the surface of the photosensitive member 1, a transfer device 5 that transfers the toner from the surface of the photosensitive member 1 to a transferee 7 at a transfer position Pd, and a cleaning device 6 that removes toner from the surface of the photosensitive member 1. The cleaning device 6 is equipped with a cleaning blade 61 that contacts the surface of the photosensitive member 1 at a blade cleaning position Pf downstream of the transfer position Pd and upstream of the charging position Pa in terms of the rotation direction of the photosensitive member 1, a rotatable roller-shaped brush 62 that contacts the surface of the photosensitive member 1 at a brush cleaning position Pe downstream of the transfer position Pd and upstream of the blade cleaning position Pf in terms of the rotation direction of the photosensitive member 1, and an application unit E5 that applies a bias to the brush 62. In this embodiment, the image forming apparatus 100 determines the tensile strength of the single brush fiber of the brush 62 under an environment of a temperature of 23° C. and a humidity of 50% as A (cn / dtex), the thickness of the single brush fiber as B (denier), and the bristle density per single brush fiber as C (kF / inch 2), the length of the brush fiber is D (mm), and the elastic deformation rate when a hardness test is performed on the surface of the photosensitive member 1 using a Vickers square pyramid diamond indenter under an environment of a temperature of 23°C and a humidity of 50% is E (%), 48 (%) ≦ E ≦ 60 (%) and 400 ≦ {A × B 2 ×C / D 2}≦20408 is satisfied. In this embodiment, when the image forming area on the surface of the photoconductor 1 passes through the brush cleaning position Pe, the bias applying unit E5 applies a bias to the brush 62 so that the potential of the brush 62 has a polarity opposite to the normal charging polarity of the toner. In this embodiment, the electrical resistance of the brush 62 is 10 Log Ω or more and 12 Log Ω or less under an environment of 23°C temperature and 50% humidity. In this embodiment, the cleaning device 6 includes a conductive member 63 that contacts the brush 62 and a removing member 64 that removes toner from the conductive member 63. The bias applying unit E5 applies a bias to the brush 62 via the conductive member 63. In this embodiment, the brush 62 rotates in the forward direction relative to the surface of the photoconductor 1 at a speed different from that of the surface of the photoconductor 1 at the contact portion with the photoconductor 1.

[0089] According to this embodiment, the life of the photosensitive drum 1 can be extended, and the occurrence of toner fusion on the surface of the photosensitive drum 1 can be suppressed.

[0090] [Example 2] Next, another embodiment of the present invention will be described. The basic configuration and operation of the image forming apparatus of this embodiment are the same as those of embodiment 1. Therefore, in the image forming apparatus of this embodiment, elements having the same or corresponding functions or configurations as those of the image forming apparatus of embodiment 1 are given the same reference numerals as those of embodiment 1, and detailed explanations thereof will be omitted.

[0091] FIG. 9 is a schematic cross-sectional view of the cleaning device 6 and its surroundings in this embodiment. In this embodiment, the image forming apparatus 100 includes a pre-cleaning static eliminator 16, which serves as a static eliminator for eliminating static electricity from the photosensitive drum 1 downstream of the primary transfer position T1 and upstream of the fur brush 62 in the rotational direction of the photosensitive drum 1. In this embodiment, the static eliminator 16 irradiates the surface of the photosensitive drum 1 with light to eliminate static electricity from the surface of the photosensitive drum 1. The static eliminator 16 irradiates the surface of the photosensitive drum 1 with light, and the position on the photosensitive drum 1 where static elimination is performed (i.e., where light is irradiated) by the static eliminator 16 in the rotational direction of the photosensitive drum 1 is the static elimination position Pi. In other words, the static elimination position Pi is located downstream of the primary transfer position Pd and upstream of the brush cleaning position Pe in the rotational direction of the photosensitive drum 1. In this embodiment, the static eliminator 16 uses an LED as a static elimination light source, but other means, such as a semiconductor laser, may also be used. In this embodiment, the static eliminator 16 uses constant current control, with the current set to 50 mA. The static eliminator 16 emits light (pre-cleaning exposure) toward the surface of the photosensitive drum 1 to eliminate the surface potential of the photosensitive drum 1. The static eliminator 16 uniformly eliminates the surface potential of the photosensitive drum 1 (at least the surface potential of the image forming area in the direction of the rotation axis) to about -100 to 0 V before the fur brush 62 electrostatically collects the toner. In this embodiment, as in the first embodiment, the charged potential of the photosensitive drum 1 is about -500 V, and the exposed potential of the photosensitive drum 1 is about -200 V. "Static elimination" refers to removing at least a portion of the electric charge.

[0092] When the voltage applied to the fur brush 62 is opposite in polarity to the normal charging polarity of the toner and the absolute value of the potential difference between the fur brush 62 and the photosensitive drum 1 is preferably 250 V or greater, the toner is electrostatically collected from the photosensitive drum 1 to the fur brush 62. On the other hand, when the absolute value of the potential difference between the fur brush 62 and the photosensitive drum 1 is equal to or greater than the discharge start voltage (e.g., 650 V), the charge polarity of the toner on the photosensitive drum 1 is reversed (reversed), making it impossible for the fur brush 62 to electrostatically collect the toner from the photosensitive drum 1. In other words, the absolute value of the potential difference between the fur brush 62 and the photosensitive drum 1 is preferably equal to or greater than 250 V but less than the discharge start voltage. The discharge start voltage can be measured using the following method. During solid white image formation, the voltage applied to the fur brush 62 is increased from 0 V, and the current flowing from the fur brush 62 to the photosensitive drum 1 is measured. At this time, the current begins to flow at a certain threshold voltage. Here, the discharge start voltage is defined as the voltage at which a current of 10 μA or more begins to flow.

[0093] If the static eliminator 16 is not provided, the potential difference between the fur brush 62 and the photosensitive drum 1 differs between the solid black image area and the solid white image area (non-image area), and the fur brush 62 may not be able to collect the toner, resulting in toner fusion. For example, in the solid white image area, the absolute value of the potential difference between the photosensitive drum 1 and the fur brush 62 exceeds the discharge start voltage, causing discharge to reverse the charge polarity of the toner on the photosensitive drum 1. In other words, in order to keep the brush stiffness index below a certain level and achieve a long lifespan of the photosensitive drum 1 as described in the first embodiment, it is important to appropriately collect the toner before it reaches the external dam layer and maintain the stability of the external dam layer to prevent toner fusion.

[0094] In contrast to this, by providing the static eliminator 16 as in this embodiment, the potential difference between the fur brush 62 and the photosensitive drum 1 is appropriately maintained, and the toner can be appropriately collected by the fur brush 62. In this embodiment, the toner can be more appropriately collected before it reaches the external dam layer, and the external dam layer can be more stably maintained, thereby suppressing the occurrence of toner fusion, and therefore it becomes easy to keep the brush stiffness index below a certain level in order to achieve a long life of the photosensitive drum 1.

[0095] Here, an experiment similar to that in the experimental example in Example 1 was conducted for a configuration without and a configuration with the static eliminator 16, with the brush applied voltage changed. That is, when 500,000 images were formed in a high-humidity and high-temperature environment (30°C / 80%), the surface condition of the photosensitive drum 1, such as abrasion and surface roughness, and the occurrence of image defects due to toner fusion were confirmed. Note that the evaluation was conducted using the black image forming unit 10K. The evaluation criteria were the same as those in the experimental example in Example 1.

[0096] The results are shown in Figure 10. From the results shown in Figure 10, it can be seen that when the static eliminator 16 is provided, the potential difference between the fur brush 62 and the photosensitive drum 1 is maintained uniform in the direction of the rotation axis of the photosensitive drum 1, which allows the toner to be more appropriately collected before it reaches the external dam layer, thereby maintaining the external dam layer more stably and suppressing toner fusion. It can also be seen that when the static eliminator 16 is provided, the range (margin) of brush applied voltage in which the potential difference between the fur brush 62 and the photosensitive drum 1 can be appropriately set and the toner can be appropriately collected by the fur brush 62 is wider than when the static eliminator 16 is not provided.

[0097] As described above, in this embodiment, the image forming apparatus 100 includes the static eliminator 16 that eliminates static electricity from the surface of the photoconductor 1 at the static elimination position Pi, which is downstream of the transfer position Pd and upstream of the brush cleaning position Pe in terms of the rotation direction of the photoconductor 1. In this embodiment, the static eliminator 16 irradiates the surface of the photoconductor 1 with light to eliminate static electricity from the surface of the photoconductor 1. In this embodiment, the application unit E5 applies a bias to the brush 62 when the image formation area on the surface of the photoconductor 1 passes through the brush cleaning position Pe, so that the potential of the brush 62 has a polarity opposite to the normal charging polarity of the toner, and so that the absolute value of the potential difference between the brush 62 and the surface of the photoconductor 1 that has been neutralized at the static elimination position Pi is less than the discharge start voltage.

[0098] According to this embodiment, the life of the photosensitive drum 1 can be extended, and the occurrence of toner fusion on the surface of the photosensitive drum can be more stably suppressed.

[0099] [others] Although the present invention has been described above with reference to specific embodiments, the present invention is not limited to the above-described embodiments.

[0100] For example, in the above-described embodiment, the rotatable roller-shaped brush is rotationally driven to move in the forward direction relative to the photosensitive member at the contact portion with the photosensitive member, but this is not limited to this. For example, the rotatable roller-shaped brush may be rotationally driven to move in the reverse direction relative to the photosensitive member at the contact portion with the photosensitive member, so as to rotate at a speed different from that of the photosensitive member. Similarly, in the above-described embodiment, the collection member (conductive member) is rotationally driven to move in the forward direction relative to the brush at the contact portion with the brush, but it may be rotationally driven to move in the reverse direction.

[0101] In addition, in Example 2, a configuration in which electricity is removed by light is used as the electricity removal means, but this is not limited to this, and it is also possible to remove electricity by, for example, AC discharge using a charger, or by dissipating charge to a conductive member in contact with the photosensitive member.

[0102] Furthermore, while the image forming apparatus in the above-described embodiment employs an intermediate transfer system, the present invention can also be applied to a direct transfer image forming apparatus. As is well known to those skilled in the art, a tandem image forming apparatus employing a direct transfer system has a recording material carrier formed of an endless belt or the like instead of the intermediate transfer member in the above-described embodiment. The toner image formed on the photosensitive member of each image forming station is then directly transferred to a recording material carried and transported on the recording material carrier, similar to the primary transfer in an intermediate transfer image forming apparatus. Applying the present invention in accordance with the above-described embodiment to such an image forming apparatus can achieve the same effects as those of the above-described embodiment.

[0103] Furthermore, in the above-described embodiment, the number of image forming units is four, but the present invention is not limited to this embodiment and can also be applied to an image forming apparatus having five or more (e.g., six) image forming units. Furthermore, in the above-described embodiment, the image forming apparatus is configured to use four colors of toner, Y, M, C, and K, but the present invention is not limited to this embodiment. The image forming apparatus may be configured to use a transparent toner or a metallic color toner in addition to Y, M, C, and K, or in place of any one of these colors.

[0104] Furthermore, in the above-described embodiment, the image forming apparatus is a color image forming apparatus having a plurality of image forming units, but the present invention can also be applied to, for example, a monochrome image forming apparatus having only one image forming unit. [Explanation of symbols]

[0105] 1 Photosensitive drum 6 Cleaning Device 16 Static eliminator 61 Cleaning blade 62 Fur Brush 63 Collection roller 64 Scraper member E5 Cleaning Power Supply

Claims

1. a rotatable photoreceptor; an image forming unit that forms a toner image on the photosensitive member; a cleaning device for cleaning the photosensitive member, the cleaning device including: a blade that comes into contact with the photosensitive member at a first contact portion and cleans the photosensitive member; and a rotatable brush that comes into contact with the photosensitive member at a second contact portion that is located upstream of the first contact portion in the rotation direction of the photosensitive member and collects toner remaining on the photosensitive member; a transfer device that transfers the toner image from the photosensitive member to a transfer material at a transfer position; a static eliminator disposed downstream of the transfer position and upstream of the second contact portion in the rotation direction of the photosensitive member, the static eliminator eliminating static electricity from the photosensitive member; an application unit that applies a bias to the brush; a control unit that controls the application unit; and the control unit controls the application unit to apply a bias to the brush when the image forming area on the surface of the photosensitive member passes through the second contact unit so that the potential of the brush has a polarity opposite to the normal charging polarity of the toner, and so that the absolute value of the potential difference between the potential of the brush and the potential of the surface of the photosensitive member neutralized by the neutralization device is 250 V or more and less than a discharge start voltage; The tensile strength of the brush is A (cn / dtex), the thickness of the brush is B (denier), and the bristle density of the brush is C (kF / inch). ２ ), the length of the brush is D (mm), and the elastic deformation rate of the surface of the photosensitive member is E (%). 48(%)≦E≦60(%), and 400≦{A×B ２ ×C / D ２ }≦20408 An image forming apparatus characterized by:

2. {A×B 2 ×C / D 2}≦13333 2. The image forming apparatus according to claim 1, wherein:

3. {A×B 2 ×C / D 2}≦8889 2. The image forming apparatus according to claim 1, wherein:

4. 2. The image forming apparatus according to claim 1, wherein the static eliminator irradiates the surface of the photosensitive member with light to eliminate static electricity from the surface of the photosensitive member.

5. 2. The image forming apparatus according to claim 1, wherein the brush has an electrical resistance of 10 Log Ω or more and 12 Log Ω or less in an environment of a temperature of 23° C. and a humidity of 50%.

6. 2. The image forming apparatus according to claim 1, further comprising: a conductive member in contact with the brush; and a removing member that removes toner from the conductive member, wherein the applying unit applies a bias to the brush via the conductive member.

7. 2. The image forming apparatus according to claim 1, wherein the brush rotates in the second contact portion in a direction parallel to the moving direction of the surface of the photosensitive member, and rotates at a speed different from that of the surface of the photosensitive member.

8. 2. The image forming apparatus according to claim 1, wherein the image forming unit includes a developing device that develops a toner image on the photosensitive member, the developing device including a developing sleeve that carries a developer containing toner and an external additive, and the external additive is supplied to the first contact portion during image formation.

9. 9. The image forming apparatus according to claim 8, wherein the external additive is charged with a polarity opposite to the normal charging polarity of the toner.

10. 10. The image forming apparatus according to claim 9, wherein the external additive is inorganic fine powder of perovskite crystal.

11. 10. The image forming apparatus according to claim 9, wherein the external additive contains silica or titanium oxide.

12. 10. The image forming apparatus according to claim 9, wherein the external additive is strontium titanate.

Images